The present invention provides: a method of manufacturing a hollow anchor with a threaded outer surface, the device for carrying out the method and the anchor made thereby.
The anchor of the present invention has many uses, but it is designed specifically to be used as a masonry anchor in construction environment where a designer would like a threaded female coupling embedded in a cementitious or other masonry member.
There are many internally threaded, female coupling anchors for cementitious members. The anchor of the present invention installs easily because it is formed with an outer thread or helical contour that allows the anchor to be driven into an unthreaded, cylindrical masonry bore. The outer, radial thread formed on the anchor taps its own thread groove in the wall of the bore, making a strong and positive attachment with the concrete member.
The anchor is particularly useful for being installed in overhead ceilings where it is difficult for workman to operate. The anchor is installed in the concrete after the concrete has set which allows for the anchor to be place exactly where it is needed, and on an as-needed basis. In overhead applications, the goal is to require as few placement steps as is necessary as working overhead can be very tiring. With the present anchor, there are only two major steps. A blind hole is drilled in the concrete with a powered driver. Preferably, the driver can be used both to drill the bore, and then the drill attachment can be removed and a driver, such as a hex head driver can be fitted. There are also drivers that can fit over drill bits on powered drivers which can be used. The hole is cleaned and then using the driver with an attachment that couples with a mating surface of the anchor, the anchor is rotatably driven into the hole. The anchor cuts its own threads in the wall of the hole or bore and is thus called a self-tapping masonry anchor.
Anchors having an internally threaded bore and a self-tapping, outer thread for use in masonry are not new in the art. U.S. Pat. No. 7,056,075, granted to Powers, teaches such an anchor. The self-tapping outer thread of U.S. Pat. No. 7,056,075 differs from the present invention in many respects, but perhaps most importantly, in U.S. Pat. No. 7,056,075, the outer thread and the inner driving portion are formed in two separate operations. A cold forming draw process is used to form the internal driving area, while in a separate step, a rolling pin is used to create the thread on the outer surface. With any self-tapping, threaded masonry anchor the proper formation of the self-tapping outer thread is critical. The ability of the anchor to make a strong connection with the masonry substrate depends soley on the way the thread or threads of the anchor interact with the masonry. Thus it is important that thread can be made accurately and that the dimensions and tolerances for the outer thread remain uniform over production runs. It is believed that particular features of the present anchor are unique and the method of manufacture provided herein allows for high quality anchors to be produced economically.
According to the method of the present invention, the outer thread is formed on a hollow blank in a non-cutting operation with the outer surface of the blank being plastically deformed by the action of radial forces generated by a mandrel inserted through the hollow blank. Not only does this method of formation allow for an anchor to be formed with a self-cutting thread that will create a strong connection with the masonry substrate, it allows the anchor to be made with unique features that further add to the quality of the connection made with the anchor.